Fix #13855: line-height animations

cc @dmethvin @gnarf37

As it turns out, we can fix line-height animations after all.

I'd also like to land an analog in 1.10.0, but it could wait for 1.10.1 if that's deemed to be the better approach since this missed beta 1.

```
   raw     gz Sizes                                                            
242403  71913 dist/jquery.js                                                   
 83348  29192 dist/jquery.min.js                                               

   raw     gz Compared to master @ 1debe49ac7d9379ede44e873e4a2ebaa10dfb0b6    
   +46    +33 dist/jquery.js                                                   
   -12     -9 dist/jquery.min.js
```